bug#18912: 24.4; mode-line corruption on graphical frames in dual-headed display

[Stefan Monnier <monnier@iro.umontreal.ca>]

> Totally disabling acceleration by using the driver's option "NoAccel",
> seems to fix the problem.

[ Told ya!  ;-)  ]

> The conclusion we reach is that it's not an Emacs bug, despite the fact
> that this weirdness only manifests in Emacs.  I never have had any
> problem with my graphics card in the 5 years of usage of this machine,
> working with any kind of application you can imagine, being the "Emacs
> bug" the only exception.

Of course, your graphics driver has probably changed over the course of
those 5 years, so maybe the driver bug simply wasn't present earlier.

Could you please open a bug-report to the maintainers of your graphics
driver and try to make sure it's fixed there?

> Just occurred to me that it might be possible for that to be a bug
> within Emacs which is only triggered when acceleration is enabled.  WDYT?

Of course it's possible.
But it seems unlikely, since AFAIK the acceleration code only affects
what/how the pixels are written but not how the X server talks to
the application.


        Stefan